Re: [PATCH 1/2] mm: prevent to add a page to swap if may_writepage is unset

[Minchan Kim <minchan@kernel.org>]

On Mon, Jan 21, 2013 at 09:39:06AM -0500, Rik van Riel wrote:
> On 01/20/2013 08:52 PM, Minchan Kim wrote:
> 
> > From 94086dc7152359d052802c55c82ef19509fe8cce Mon Sep 17 00:00:00 2001
> >From: Minchan Kim <minchan@kernel.org>
> >Date: Mon, 21 Jan 2013 10:43:43 +0900
> >Subject: [PATCH] mm: Use up free swap space before reaching OOM kill
> >
> >Recently, Luigi reported there are lots of free swap space when
> >OOM happens. It's easily reproduced on zram-over-swap, where
> >many instance of memory hogs are running and laptop_mode is enabled.
> >He said there was no problem when he disabled laptop_mode.
> >The problem when I investigate problem is following as.
> >
> >Assumption for easy explanation: There are no page cache page in system
> >because they all are already reclaimed.
> >
> >1. try_to_free_pages disable may_writepage when laptop_mode is enabled.
> >2. shrink_inactive_list isolates victim pages from inactive anon lru list.
> >3. shrink_page_list adds them to swapcache via add_to_swap but it doesn't
> >    pageout because sc->may_writepage is 0 so the page is rotated back into
> >    inactive anon lru list. The add_to_swap made the page Dirty by SetPageDirty.
> >4. 3 couldn't reclaim any pages so do_try_to_free_pages increase priority and
> >    retry reclaim with higher priority.
> >5. shrink_inactlive_list try to isolate victim pages from inactive anon lru list
> >    but got failed because it try to isolate pages with ISOLATE_CLEAN mode but
> >    inactive anon lru list is full of dirty pages by 3 so it just returns
> >    without  any reclaim progress.
> >6. do_try_to_free_pages doesn't set may_writepage due to zero total_scanned.
> >    Because sc->nr_scanned is increased by shrink_page_list but we don't call
> >    shrink_page_list in 5 due to short of isolated pages.
> >
> >Above loop is continued until OOM happens.
> >The problem didn't happen before [1] was merged because old logic's
> >isolatation in shrink_inactive_list was successful and tried to call
> >shrink_page_list to pageout them but it still ends up failed to page out
> >by may_writepage. But important point is that sc->nr_scanned was increased
> >although we couldn't swap out them so do_try_to_free_pages could set
> >may_writepages.
> >
> >Since [1] was introduced, it's not a good idea any more to depends on
> >only the number of scanned pages for setting may_writepage. So this patch
> >adds new trigger point of setting may_writepage as below DEF_PRIOIRTY - 2
> >which is used to show the significant memory pressure in VM so it's good
> >fit for our purpose which would be better to lose power saving or clickety
> >rather than OOM killing.
> >
> >[1] f80c067[mm: zone_reclaim: make isolate_lru_page() filter-aware]
> >
> >Reported-by: Luigi Semenzato <semenzato@google.com>
> >Signed-off-by: Minchan Kim <minchan@kernel.org>
> 
> Your patch is a nice simplification.  I am ok with the
> change, provided it works for Luigi :)

Thanks, Rik.

Oops, I missed to Ccing Luigi. Add him again.
Luigi, Could you test this patch?
Thanks for your endless effort.

> 
> Acked-by: Rik van Riel <riel@redhat.com>
> 
> 
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-- 
Kind regards,
Minchan Kim

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